This invention generally relates to a safety device for a vehicle wheel indicator, and specifically to a device for detecting relative movement between a wheel hub and a wheel.
In large vehicles and especially a tractor-trailer, it is possible for flat tires and other wheel problems to go unnoticed. Detection of deteriorating wheel conditions is difficult due to the distance between the operator and the wheels of the vehicle. A tractor-trailer typically includes four wheels mounted to each axle. This configuration causes difficulty in detecting tire problems.
Often wheel problems are the result of failure of wheel studs that secure a wheel to the axle. Typically, wheel studs fracture because of improper tightening. An improperly tightened lug nut can cause increased fatigue stresses that can result in premature wheel stud failure. Further, contaminants lodged between the wheel and the hub mounting surface prevent proper seating of the wheel. Improper seating results in improper tightening of the lugnuts. In each instance, the vehicle operator often has little or no warning of a failure.
Improper tightening of wheel studs is recognized as a contributor to premature failure and many devices are available for detecting improper lug nut torque. One such device includes a cover corresponding to each lug nut and press fit onto each lug nut to prevent loosening. Another device includes a pointer that provides a visual indication that a lug nut has rotated away from a properly tightened position. These devices all depend on preventing or detecting rotation of the lug nuts to indicate a wheel loosening condition. However, in some instances, the lug nuts may not loosen before a wheel stud failure. Contaminants between the wheel and the mounting surface may prevent complete and proper seating of the wheel on the hub. Contaminants trapped between the wheel hub and wheel may break away during operation, resulting in a loose wheel. Under these conditions, detection of lug nut position is not a reliable means of detecting a loose wheel condition.
Wheel separation results when wheel studs fail due to stresses caused by relative movement between the hub and the wheel. Movement of the wheel relative to the hub will eventually cause fracture and failure of the mounting studs of the wheel.
Accordingly, it is desirable to develop a method and device for detecting relative motion between a wheel and hub and warn of a loose wheel condition.